Hello,

Thank you for your query.

I am so sorry to know that your child has an arachnoid cyst in his brain.

It is obvious that it is a congenital anomaly for your child,
It is a sac collection of fluid covered by meninges between the brain matter & base of the skull.
In most of the cases these are asymptomatic.
But neurological features may develop in case of a large cyst.
It depends on the site of brain involvement.

The recent symptoms of your child may be due to the mass effect of the cyst.
But proper physical examination is required to exclude any other neurological problem.

There are various treatment options.
But all of them are surgical.

At this moment consultation with a neurosurgeon is very essential.

I hope I was of some help.

Please write if you have any doubt.

Take care.

---